Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 12 The Cell Cycle

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Unicellular organisms – Reproduce by cell division 100 µm (a) Reproduction. An amoeba, a single-celled eukaryote, is dividing into two cells. Each new cell will be an individual organism (LM). Figure 12.2 A

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Multicellular organisms depend on cell division for – Development from a fertilized cell – Growth – Repair 20 µm200 µm (b) Growth and development. This micrograph shows a sand dollar embryo shortly after the fertilized egg divided, forming two cells (LM). (c) Tissue renewal. These dividing bone marrow cells (arrow) will give rise to new blood cells (LM). Figure 12.2 B, C

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cell Reproduction a.Def – formation of 2 daughter cells from a parent cell b.B. Types 1. Binary fission- prokaryotes 2. Mitosis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 1. Binary fission In binary fission – The bacterial chromosome replicates – The two daughter chromosomes actively move apart Origin of replication E. coli cell Bacterial Chromosome Cell wall Plasma Membrane Two copies of origin Origin Chromosome replication begins. Soon thereafter, one copy of the origin moves rapidly toward the other end of the cell. 1 Replication continues. One copy of the origin is now at each end of the cell. 2 Replication finishes. The plasma membrane grows inward, and new cell wall is deposited. 3 Two daughter cells result.4 Figure 12.11

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2. Mitosis a. Form of nuclear division that maintains the chromosome number b. Part of the cell cycle c. Carried out by eukaryotic cells

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings What is the cell cycle? The time the cell spends growing and dividing * Most time spent in interphase INTERPHASE G1G1 S (DNA synthesis) G2G2 Cytokinesis Mitosis MITOTIC (M) PHASE Figure 12.5

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cell cycle phases 1.Interphase (lots of time) a. G1 (inc size, prepares for S phase) b. S phase (DNA synthesis) c. G2 (prepares to divide) 2.Mitosis (little time) a. mitosis b. cytokinesis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cell cycle cont Cellular organization of DNA 1. Genome – cell’s DNA 2. Chromosomes (when condensed) 3. Chromatin – complex of DNA & associated proteins

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mitosis Steps 1.Prophase 2.Prometaphase 3.Metaphase 4.Anaphase 5.Telophase and Cytokinesis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mitosis Steps 1.Prophase a. Chromo condense (sister chromatids) b. Spindle fibers begin to form c. Nuclear envelope breaks up into small vesicles

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sister chromatids Each duplicated chromosome – Has two sister chromatids, which separate during cell division 0.5 µm Chromosome duplication (including DNA synthesis) Centromere Separation of sister chromatids Sister chromatids Centromeres Sister chromatids A eukaryotic cell has multiple chromosomes, one of which is represented here. Before duplication, each chromosome has a single DNA molecule. Once duplicated, a chromosome consists of two sister chromatids connected at the centromere. Each chromatid contains a copy of the DNA molecule. Mechanical processes separate the sister chromatids into two chromosomes and distribute them to two daughter cells. Figure 12.4

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mitosis steps 2.Prometaphase Condensed chromosomes are “hooked” on to spindle fiber “hooked” on a kinetochore (a specialized protein structure located at centromere)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mitosis consists of five distinct phases – Prophase – Prometaphase G 2 OF INTERPHASE PROPHASE PROMETAPHASE Centrosomes (with centriole pairs) Chromatin (duplicated) Early mitotic spindle Aster Centromere Fragments of nuclear envelope Kinetochore Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Kinetochore microtubule Figure 12.6 Nonkinetochore microtubules

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mitosis steps 3.Metaphase – chromosomes are pulled in opposite directins by contracting spindle finbers & line cell equator 4.Anaphase – a. Centromeres of each duplicated chromosome “snap” b. Sister chromatids separated to become unduplicated chromosomes Over when chromo reach the poles

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – Metaphase – Anaphase – Telophase Centrosome at one spindle pole Daughter chromosomes METAPHASEANAPHASETELOPHASE AND CYTOKINESIS Spindle Metaphase plate Nucleolus forming Cleavage furrow Nuclear envelope forming Figure 12.6

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mitosis Steps cont 4.Telophase a. begins when unduplicated chromo poles b. Chromosomes decondense c. Nuclear membrane reforms d. Usually cytokinesis occurs (cytoplasmic division)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cytokinesis 1. animal – “pinch center 2. plant – cell plate formation

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cytokinesis: A Closer Look In animal cells – Cytokinesis occurs by a process known as cleavage, forming a cleavage furrow Cleavage furrow Contractile ring of microfilaments Daughter cells 100 µm (a) Cleavage of an animal cell (SEM) Figure 12.9 A

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In plant cells, during cytokinesis – A cell plate forms Daughter cells 1 µm Vesicles forming cell plate Wall of patent cell Cell plate New cell wall (b) Cell plate formation in a plant cell (SEM) Figure 12.9 B

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mitosis in a plant cell 1 Prophase. The chromatin is condensing. The nucleolus is beginning to disappear. Although not yet visible in the micrograph, the mitotic spindle is staring to from. Prometaphase. We now see discrete chromosomes; each consists of two identical sister chromatids. Later in prometaphase, the nuclear envelop will fragment. Metaphase. The spindle is complete, and the chromosomes, attached to microtubules at their kinetochores, are all at the metaphase plate. Anaphase. The chromatids of each chromosome have separated, and the daughter chromosomes are moving to the ends of cell as their kinetochore microtubles shorten. Telophase. Daughter nuclei are forming. Meanwhile, cytokinesis has started: The cell plate, which will divided the cytoplasm in two, is growing toward the perimeter of the parent cell Nucleus Nucleolus Chromosome Chromatine condensing Figure 12.10

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Cell Cycle Control System The sequential events of the cell cycle – Are directed by a distinct cell cycle control system, which is similar to a clock Figure Control system G 2 checkpoint M checkpoint G 1 checkpoint G1G1 S G2G2 M

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The clock has specific checkpoints – Where the cell cycle stops until a go-ahead signal is received G 1 checkpoint G1G1 G1G1 G0G0 (a) If a cell receives a go-ahead signal at the G 1 checkpoint, the cell continues on in the cell cycle. (b) If a cell does not receive a go-ahead signal at the G 1 checkpoint, the cell exits the cell cycle and goes into G 0, a nondividing state. Figure A, B

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Loss of Cell Cycle Controls in Cancer Cells Cancer cells – Do not respond normally to the body’s control mechanisms – Form tumors

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Malignant tumors invade surrounding tissues and can metastasize – Exporting cancer cells to other parts of the body where they may form secondary tumors Cancer cells invade neighboring tissue. 2 A small percentage of cancer cells may survive and establish a new tumor in another part of the body. 4 Cancer cells spread through lymph and blood vessels to other parts of the body. 3 A tumor grows from a single cancer cell. 1 Tumor Glandular tissue Cancer cell Blood vessel Lymph vessel Metastatic Tumor Figure 12.19